1. Field of the Art
The present invention relates to a method for controlling the permeability of a gas to be separated in a process of separating gasses by an organic separation membrane, characterized in that the method comprises irradiating the organic separation membrane with a microwave to alter the structure of the organic separation membrane; and a method for producing an organic separation membrane, characterized in that the method comprises irradiating the organic separation membrane with a microwave in a process of producing the organic separation membrane, thereby altering the structure of the organic separation membrane to control the permeability of a gas.
2. Description of the Related Art
Membrane separation processes which are currently known are used practically and applied utilizing several principles on membrane separation. The principles can be classified on the basis of driving forces and mechanisms of separation. The driving forces include static pressure difference, concentration difference, potential difference, partial pressure difference and the like, and the mechanisms of separation include sieving effect by pores, difference in adsorptivity, physicochemical exclusion of elute, difference in diffusion coefficients, difference in signs of ionic charges, difference in partition coefficient, difference in incorporation by supports, difference in releasing rates and the like.
In addition, kinds of separation membranes, structural control and producing methods have been devised depending on gasses to be separated in gas membrane separation process in order to exert the driving forces and mechanisms of separation at the maximum level. In these devices, the permeability of a gas through a separation membrane is altered by controlling the size, shape, distribution and density of pores on the separation membrane, the chemical structure, crystal structure and charge density of materials for the separation membrane by the use of several materials for membrane and producing methods. That is, methods for controlling permeability which are currently used are based mainly on the development of novel materials for membrane and the combination of the exiting techniques.
On the other hand, It is proposed that a membrane separation process based on a new concept which comprises controlling the permeability of a substance by controlling the opening and closing of molecular valve externally by electric stimulation. Such a membrane separation process includes, for example the one reported in Polymer Gels and Networks, Vol. 1, 247-255, 1993.
JP-A-63-201607 (1987) disclosed a method of regulating the permeability of the fluid permeable membrane for gas or liquid. In the method, the high frequency generator is connected to the membrane by clamps so that dielectric dispersion causes the membrane to be permeable to fluid.
However, at the present stage little is known about the development of membrane separation process based on a new concept other than the above mentioned one.
As a result that the present inventors researched eagerly, they found that irradiation to a separation membrane composed of an organic material with a microwave can alter the structure of a molecule or a domain thereof constituting the organic separation membrane externally to control the permeability of a gas to be separated (hereinafter, referred to as an external operation of molecular valve), and completed the present invention. For example, in a case of an organic separation membrane composed of cellulose acetate, when the organic separation membrane is irradiated with a microwave, an acetyl group that is a side group bonded to the cellulose skeleton starts to vibrate or rotate, or change the orientation thereof, thereby increasing or decreasing a part that a gas to be separated is permeable in the molecular structure, a so lied the size of molecular pores. And, the permeability of the gas to be separated is altered according to an increase or decrease in the size of the molecular pores.
Further, the present inventors found that the permeability of a gas through an organic separation membrane can be controlled by irradiating the organic separation membrane with a microwave in the production of the organic separation membrane.
Therefore, the present invention relates to the following aspects:
as first aspect, a method for controlling a permeability of a gas to be separated through an organic separation membrane in a separation process of gasses by an organic separation membrane, characterized in that the method comprises irradiating the organic separation membrane with a microwave to cause vibration/rotation of a molecule or a domain thereof constituting the organic separation membrane and alter the structure and/or polarity of the organic separation membrane, and thus altering a permeability of the gas to be separated;
as a second aspect, the method as set forth in the first aspect wherein the separation process is any one selected from a group consisting of gas permeation and pervaporation;
as a third aspect, the method as set forth in the first aspect, wherein the separation process is gas permeation;
as a fourth aspect, the method as set forth in the first aspect, wherein the organic separation membrane is any one selected from a group consisting of a densified membrane, a porous membrane, a complex membrane, a sintered polymer membrane, an oriented polymer membrane and an ion exchange membrane;
as a fifth aspect, a method for producing an organic separation membrane, characterized by irradiating with a microwave in a process of producing the organic separation membrane to control a permeability of the organic separation membrane;
as a sixth aspect, a method for producing an organic separation membrane, characterized in that the method comprises forming an organic separation membrane and then irradiating the resulting organic separation membrane with a microwave to control a permeability of the organic separation membrane;
as a seventh aspect, the method as set forth in the fifth aspect, wherein the organic separation membrane is any one selected from a group consisting of a densified membrane, a porous membrane, a complex membrane, a sintered polymer membrane, an oriented polymer membrane and an ion exchange membrane; and
as an eighth aspect, the method as set forth in the sixth aspect, wherein the organic separation membrane is any one selected from a group consisting of a densified membrane, a porous membrane, a complex membrane, a wintered polymer membrane, an oriented polymer membrane and an ion exchange membrane.
The external operation of molecular valve by Irradiating with a microwave in the present invention has not known at all in the process of separating gasses, and this may be attributable to that it is difficult to design an apparatus therefor.
Further, conventionally, it has not been known 1) to irradiate with a microwave in a process of forming a membrane and control the structure itself of the membrane, 2) nor to control the structure of a membrane formed in advance by irradiating the structure of the membrane with a microwave.